1. Field of the Invention
The present invention relates to a thermal transfer element and, more particularly, to a thermal transfer element capable of improving transfer characteristics by performing thermal transfer at a low temperature.
2. Description of the Related Art
In general, an organic electroluminescent display device (OLED) includes an anode electrode formed on an insulating substrate as a lower electrode, an organic thin film layer formed on the anode electrode, and a cathode electrode formed on the organic thin film layer as an upper electrode. The organic thin film layer includes at least one of a hole injection layer, a hole transport layer, an emission layer, a hole blocking layer, an electron transport layer and an electron injection layer.
A method of forming the organic thin film layer may be a deposition method or a lithography method. The deposition method is a method of forming an organic emission layer by vacuum depositing an organic electroluminescent material using a shadow mask, but it is difficult to form a fine pattern due to deformation of the mask and difficulty in applying it to a large-sized display device. The lithography method is a method of forming an organic emission layer by depositing an organic electroluminescent material and then patterning the organic electroluminescent material using a photoresist material, and this method is capable of forming a fine pattern. However, the lithography method has the problem of deterioration of the characteristics of the organic emission layer due to use of a developer or an etchant of the organic electroluminescent material used to form a photoresist pattern.
In order to solve these problems, an inkjet method for directly patterning an organic emission layer has been proposed. The inkjet method is a method of forming an organic emission layer by ejecting an electroluminescent material solved or dispersed in solvent from the head of an inkjet printer device. The inkjet method uses a relatively simple process, but the yield is lowered and/or the thickness of the layer is irregular, and it is difficult to apply this method to a large-sized display device.
A method of forming an organic emission layer using a thermal transfer method as a dry etching process has also been proposed. The thermal transfer method is a method of forming R, G and B organic emission layers by converting light emitted from a light source into thermal energy, and transferring an image forming material to an insulating substrate using the thermal energy.
Laser thermal transfer technology is technology involving transfer of a color ink material using a laser, which transfers a thermal transfer element to a body by laser-irradiating the thermal transfer element. The thermal transfer element has an image transfer layer on which materials, such as dyes, paints or the like, to be transferred are applied. Therefore, a donor film is very important, the donor film being a thermal transfer element capable of stably and effectively transferring the image by means of the laser thermal transfer method, which requires much energy to transfer the image.